Oct-ivus catheter for concurrent luminal imaging

ABSTRACT

The invention relates to an apparatus for in vivo imaging. More specifically, the present invention relates to a catheter that incorporates an Optical Coherence Tomography (OCT) system and an Intravascular Ultrasound (“IVUS) system for concurrent imaging of luminal systems, such as imaging the vasculature system, including, without limitation, cardiac vasculature, peripheral vasculature and neural vasculature.

CROSS-REFERENCE TO RELATED INVENTIONS

This application claims priority pursuant to 35 U.S.C. § 119(e) fromU.S. Provisional Application Ser. Nos. 60/949,472 and 60/949,511, bothfiled Jul. 12, 2007 and incorporated by reference herein.

BACKGROUND OF THE INVENTION

The present invention relates generally to an apparatus for in vivoimaging. More particularly, the present invention relates to a catheterthat incorporates an Optical Coherence Tomography (OCT) system and anIntravascular Ultrasound (IVUS) system for concurrent imaging of luminalsystems, such as imaging the vasculature system, including, withoutlimitation, cardiac vasculature, peripheral vasculature and neuralvasculature.

Myocardial infarction or heart attack remains the leading cause of deathin society. Until recently, many investigators believed that the primarymechanism for myocardial infarction was coronary arteries criticallyblocked with atherosclerotic plaque that subsequently progressed tototal occlusion. Recent evidence from many investigational studies,however, clearly indicates that most infarctions are caused by suddenrupture of non-critically stenosed coronary arteries resulting fromsudden plaque rupture. For example, Little et al. (Little, W C, Downes,T R, Applegate, R J. The underlying coronary lesion in myocardialinfarction: implications for coronary angiography. Clin Cardiol 1991,14: 868-874, incorporated by reference herein) observed thatapproximately 70% of patients suffering from an acute plaque rupturewere initiated on plaques that were less than 50% occluded as revealedby previous coronary angiography. This and similar observations havebeen confirmed by other investigators (Nissen, S. Coronary angiographyand intravascular ultrasound. Am J Cardiol 2001, 87 (suppl): 15A-20 A,incorporated by reference herein).

The development of technologies to identify these unstable plaques holdsthe potential to decrease substantially the incidence of acute coronarysyndromes that often lead to premature death. Unfortunately, no methodsare currently available to the cardiologist that may be applied tospecify which coronary plaques are vulnerable and thus prone to rupture.Although treadmill testing has been used for decades to identifypatients at greater cardiovascular risk, this approach does not have thespecificity to differentiate between stable and vulnerable plaques thatare prone to rupture and frequently result in myocardial infarction.Inasmuch as a great deal of information exists regarding the pathologyof unstable plaques (determined at autopsy), technologies based uponidentifying the well-described pathologic appearance of the vulnerableplaque offers a promising long term strategy to solve this problem.

The unstable plaque was first identified and characterized bypathologists in the early 1980's. Davis noted that with thereconstruction of serial histological sections in patients with acutemyocardial infarctions associated with death, a rupture or fissuring ofathermanous plaque was evident (Davis M J, Thomas A C. Plaque fissuring:the cause of acute myocardial infarction, sudden death, and crescendoangina. Br Heart J 1985; 53: 3 63-37 3, incorporated by referenceherein). Ulcerated plaques were further characterized as having a thinfibrous cap, increased macrophages with decreased smooth muscle cellsand an increased lipid core when compared to non-ulceratedatherosclerotic plaques in human aortas (Davis M J, Richardson E D,Woolf N. Katz O R, Mann J. Risk of thrombosis in human atheroscleroticplaques: role of extracellular lipid, macrophage, and smooth muscle cellcontent, incorporated by reference herein). Furthermore, no correlationin size of lipid pool and percent stenosis was observed when imaging bycoronary angiography. In fact, most cardiologists agree that unstableplaques progress to more stenotic yet stable plaques through progressionvia rupture with the formation of a mural thrombus and plaqueremodeling, but without complete luminal occlusion (Topol E J, RabbaicR. Strategies to achieve coronary arterial plaque stabilization.Cardiovasc Res 1999; 41: 402-417, incorporated by reference herein).Neovascularization with intra-plaque hemorrhage may also play a role inthis progression from small lesions, i.e., those less than about 50%occluded, to larger significant plaques. Yet, if the unique features ofunstable plaque could be recognized by the cardiologist and thenstabilized, a dramatic decrease may be realized in both acute myocardialinfarction and unstable angina syndromes, and in the sudden progressionof coronary artery disease.

The present invention uses depth-resolved light reflection or OpticalCoherence Tomography to identify the pathological features that havebeen identified in the vulnerable plaque. In OCT, light from a broadband light source or tunable laser source is split by an optical fibersplitter with one fiber directing light to the vessel wall and the otherfiber directing light to a reference mirror. The distal end of theoptical fiber is interfaced with a catheter for interrogation of thecoronary artery during a heart catheterization procedure. The reflectedlight from the plaque is recombined with the signal from the referencemirror forming interference fringes (measured by a photovoltaicdetector) allowing precise depth-resolved imaging of the plaque on amicron scale.

OCT uses a superluminescent diode source or tunable laser sourceemitting a 400-2000 nm wavelength, with a 50-250 nm band width(distribution of wave length) to make in situ tomographic images withaxial resolution of 2-20 μm and tissue penetration of 2-3 mm. OCT hasthe potential to image tissues at the level of a single cell. In fact,the inventors have recently utilized broader bandwidth optical sourcesso that axial resolution is improved to 4 um or less. With suchresolution, OCT can be applied to visualize intimal caps, theirthickness, and details of structure including fissures, the size andextent of the underlying lipid pool and the presence of inflammatorycells. Moreover, near infrared light sources used in OCT instrumentationcan penetrate into heavily calcified tissue regions characteristic ofadvanced coronary artery disease. With cellular resolution, applicationof OCT may be used to identify other details of the vulnerable plaquesuch as infiltration of monocytes and macrophages. In short, applicationof OCT can provide detailed images of a pathologic specimen withoutcutting or disturbing the tissue.

An OCT catheter to image coronary plaques has been built and iscurrently being tested by investigators. (Jang I K, Bouma B E, Hang O H,et al. Visualization of coronary atherosclerotic plaques in patientsusing optical coherence tomography: comparison with intravascularultrasound. JACC 2002; 3 9: 604-609, incorporated by reference herein).The prototype catheter consists of a single light source and is able toimage over a 360 degree arc of a coronary arterial lumen by rotating ashaft that spins the optical fiber. Because the rotating shaft is housedoutside of the body, the spinning rod in the catheter must rotate withuniform angular velocity so that the light can be focused for equalintervals of time on each angular segment of the coronary artery.

While OCT imaging provides high resolution (2-20 μm) tomographicvisualization of coronary arteries, OCT, however, lacks penetration witha maximum penetration depth of only 2-3 mm into the tissue. The presentinvention overcomes this disadvantage by incorporating an ultrasoundtransducer suitable for performing intravascular ultrasound (“IVUS”)into an OCT catheter to form an OCT-IVUS catheter. The present inventionuses IVUS imaging to identify the pathological features that have beenidentified in the vulnerable plaque. A particularly valuable tool, IVUStechnology uses high frequency sound waves to detect blood vesselblockages and other problems such as aneurysms.

Ultrasound imaging systems can be equipped with a 38 mm aperture,broadband (5-10 MHz) linear array transducer. Cells can be imaged incolor power Doppler, power Doppler, M-mode and B-scan modes. B-scansonogram images, also called the grayscale mode, are the typicalultrasound method to monitor or examine the human body usingbackscattering of acoustic waves. M-mode ultrasound employs a sequenceof scans at a fixed ultrasound beam over a given time period. M-mode isused for visualizing rapidly moving subjects, such as heart valves.Compared to conventional B-scan images, Doppler ultrasound is used toassess changes in the frequency of reflected acoustic waves. Color powerDoppler converts reflected acoustic waves that are Doppler shifted intocolors that overlay the conventional B-scan images and can indicate thespeed and direction of moving objects. Power Doppler ultrasound is mostcommonly used to evaluate moving objects and has higher sensitivity thanthe color power Doppler mode. The gain of the color power and Dopplerimaging mode can be manually adjusted to suppress the background noise.If the settings of the ultrasound instrumentation remain unchanged,objective comparisons of each can be made. Additional disclosureexplaining how OCT and ultrasound imaging systems work and cooperate canbe found in commonly assigned and co-pending U.S. patent applicationSer. No. 11/550,771, filed Oct. 18, 2006 and published as U.S.Publication No. US 2008-0097194 on Apr. 24, 2008, which is incorporatedherein by reference in its entirety.

IVUS is a widely available clinical tool for guiding percutaneousinterventions and/or intraluminal imaging. While IVUS uses frequenciesfrom 20 to 40 MHz and provides good depth penetration, it lackssufficient resolution (˜120 μm) to study thin-cap thrombus or atheromalesions and other fine details with the vasculature. Conversely, whileOCT provides high resolution (2-20 μm) tomographic visualization ofcoronary arteries, OCT, however, lacks penetration with a maximumpenetration depth of only 2-3 mm. However, it has been found that OCTcan image behind calcifications clearly while ultrasounds are intenselyreflected. The current high resolution capabilities of OCT are wellsuited for imaging vulnerable plaques but poor depth penetration hamperfull characterization of coronary lesions and plaque burden. BecauseIVUS penetrates deeper into the media and adventitia, combining OCT andIVUS modalities will enhance quantitative analysis of coronary arteriessignificantly.

SUMMARY OF THE INVENTION

The present invention relates to a catheter that incorporates an OpticalCoherence Tomography (OCT) system and an Intravascular Ultrasound(“IVUS) system for concurrent imaging of luminal systems, such asimaging the vasculature system, including, without limitation, cardiacvasculature, peripheral vasculature and neural vasculature. An OCTassembly and an IVUS transducer are positioned at the distal end of thecatheter.

A combined OCT and IVUS catheter imaging system has been developed toprovide cross-sectional structural images of blood vessels, includingcoronary arteries. A catheter assembly surrounding an OCT assembly andan IVUS transducer at the distal end of an imaging core is used toaccomplish such imaging. The catheter assembly is positioned within ablood vessel at the site of interest (i.e., the location of a stenosis).The OCT assembly and IVUS transducer generate a series of pulses whichare transmitted outward from the OCT assembly and the IVUS transducer asthey are rotated. Echo pulses reflected from the surrounding tissues arereceived by the OCT assembly and the IVUS transducer and collected by acontrol apparatus coupled to the proximal end of the sheath. Thecollected data is then combined, transformed, and displayed as across-sectional image of the vessel and surrounding tissue.

The scope of the invention is indicated in the appended claims. It isintended that all changes or modifications within the meaning and rangeof equivalents are embraced by the claims.

The foregoing and other features and advantages of the invention areapparent from the following detailed description of exemplaryembodiments, read in conjunction with the accompanying drawings. Thedetailed description and drawings are merely illustrative of theinvention rather than limiting, the scope of the invention being definedby the appended claims and equivalents thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic side view of the present invention's OCT-IVUSsystem.

FIG. 2 is a side view of an actuation system for rotating the OCT-IVUScatheter in accordance with the present invention.

FIG. 3 is a side view of the distal end optics of the OCT assembly inaccordance with the present invention taken from circle 3 in FIG. 1.

FIG. 4 is a side view of the distal end optics and ultrasound transducerof one embodiment of the invention.

FIG. 5 is a side view of the distal end optics and ultrasound transducerof another embodiment of the invention.

FIG. 6 is perspective view of a combined ferrule-ultrasound transducerin accordance with an embodiment of the present invention.

FIG. 7 is a side view of the distal end optics and ultrasound transducerof another embodiment of the invention.

FIG. 8 is a perspective view of one embodiment of an optical fiber inaccordance with the present invention.

FIG. 9 is a perspective view of another embodiment of an optical fiberin accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the accompanying figures, like elements are identified by likereference numerals among the several preferred embodiments of thepresent invention.

In the present invention, a distal end assembly including an ultrasoundtransducer 120 and an optical coherence tomography (“OCT”) opticalassembly (as hereinafter described) are positioned longitudinallyadjacent or in close proximity to each other at or near a distal end ofa catheter assembly 111. Both the ultrasound transducer 120 and the OCToptical assembly are coupled to a rotary drive system (as hereinafterdescribed) that rotates both the OCT optical assembly and ultrasoundtransducer 120 about their longitudinal axis and within a cathetersheath. In use, the OCT-IVUS catheter assembly 111 is carefullymaneuvered through a patient's body to a point of interest such aswithin a blood vessel to position the distal end in imaging proximitywith the point of interest.

The ultrasound transducer 120 may be a single-element crystal or probethat is mechanically scanned or rotated back and forth to cover a sectorover a selected angular range. OCT and acoustic signals are thentransmitted and echoes (or backscatter) from these OCT and acousticsignals are received. The ultrasound transducer 120 and the OCT assemblymay be oriented to direct their respective energies such that theoptical signal and the ultrasound signal scan the same or at leastpartially overlapping spatial areas. Alternatively, the optical signaland the ultrasound signal may be aligned by employing appropriatecomputer processing software to adjust for spatial discrepancies betweenthe two signals and permit simultaneous display of at least partiallycoordinated optical images and the ultrasound images to the physician.The backscatter data can be used to identify the type of a scannedtissue. As the probe is swept through the sector, many OCT and acousticlines are processed building up a sector-shaped image of the patient.After the data is collected, an image (e.g., a combined OCT and IVUSimage) of the blood vessel and any associated intraluminal structures,such as plaque, thrombus, stent, etc., can be reconstructed usingwell-known techniques. This image is then visually analyzed by aphysician to assess the vessel components and plaque content.

Image analysis of data collected from use of the present inventionincludes determining the size of the lumen and amount of plaque in thevessel. This is performed by generating an image of the vessel (e.g.,combined OCT and IVUS image) and manually drawing contoured boundarieson the image where the clinician believes the luminal and themedial-adventitial borders are located. In other words, the luminalborder, which demarcates the blood-intima interface, and themedial-adventitial border, which demarcates the external elasticmembrane or the boundary between the media and the adventitia, aremanually drawn to identify the plaque-media complex that is locatedthere between.

As illustrated generally in FIG. 1, the OCT-IVUS system 100 of thepresent invention includes a proximal end and a distal end. The proximalend of the OCT-IVUS system 100 includes a rotary optical fiber connector101, sometimes also referred to in the art as a fiber optical rotaryjoint (“FORJ”). The optical fiber connector 101 joins two opticalfibers, one optical fiber 105 that is stationary and proximal to theoptical fiber connector 101 and another optical fiber 106 that isrotatable and distal to the optical fiber connector 101. Different typesof optical fiber connectors 101, e.g., SC-APC plug-in connector, havebeen developed in the art for various applications and are encompassedby the present invention. A distal end catheter assembly 111, shown ingreater detail in FIG. 3, consists generally of the OCT optical assemblyand the ultrasound transducer 120 positioned with a housing 110, that iscoupled at its proximal end to a rotary drive shaft 104, that, in turn,is coupled to a rotary drive actuator, such as that illustrated in anddescribed with reference to FIG. 2.

Turning to FIG. 2, a rotary actuation system, which includes a rotarymotor 102, an optical fiber connector 101, and gears 103, is illustratedrotating a driveshaft 104. The driveshaft 104 itself is comprised of afitting (not shown) that overlies and houses the optical fiber 106distal to the optical fiber connector 101. This rotary actuation systemmay also include a linear actuation system (not shown) to facilitatemanual or automated pull-back of the catheter.

FIG. 3 provides a closer side view of the distal end of the OCT-IVUSsystem 100 depicted in FIG. 1. The catheter assembly 111 includes anouter catheter sheath 113 that terminates at a distal end thereof in adistal tip 120 having a guidewire lumen 161 configured for rapidguidewire exchange. The outer catheter sheath 113 is preferably at leastpartially, preferably near totally, transparent to both optical andultrasound energy to permit transmission of optical and ultrasonicenergy to and from the IVUS-OCT catheter assembly 111. Co-pending,commonly assigned U.S. Provisional Patent Application Ser. No.60/949,511, filed Jul. 12, 2007, from which priority is claimed,describes a monolithic catheter construct and rotary drive systemwell-suited for use with the present invention, and is herebyincorporated by reference thereto as if fully set forth herein.

A driveshaft 104 extends from the proximal end of the OCT-IVUS system100 into the catheter assembly 111. In one embodiment, the outer surfaceof the catheter assembly 111 is covered and protected by an outer sheathformed of PFA (perfluoroalkoxy). To avoid damage to blood vessels,sheaths may also be formed of other flexible plastic-type materials,having high hoop strengths or with reinforcements, to help stop thiskinking and bending while reducing tissue damage during catheterintroduction. Other appropriate materials known in the art for use as anouter sheath are also within the scope of the present invention.

The catheter assembly 111 includes, but is not limited to, a protectionbearing 110, a ferrule 114, a GRIN lens assembly 116, a prism 118, anOCT imaging port 117, an optical fiber 106, and an IVUS transducer 120,all of which are housed within the protection bearing 110.

The catheter assembly 111 may also include a rapid exchange section 160which has a guidewire lumen 161 that extends between a guidewireentrance port 162 and a guidewire exit port 164. The protection bearing110 serves as shield for OCT and IVUS components. The protection bearing110 is preferably a tubular housing and may be formed of metal or othersuitable material. The protection bearing 110 has at least onetransparent portion 117, which is preferably an opening through theprotection bearing 110 that is transparent to both optical andultrasonic energy to permit transmission of such energy to and from theOCT optical system and the ultrasound transducer 110. The at least onetransparent portion 117 may be positioned through a wall of theprotection bearing 110 or through an end of the protection bearing 110.

FIG. 4 illustrates one embodiment of the invention, wherein anultrasound transducer 120 is positioned proximal to the OCT assembly(i.e., ferrule 114, GRIN lens assembly 116, and prism 118). In thisembodiment, the ultrasound transducer 120 possesses a cylindricalstructure with a hollow core to provide access for an optical fiber 106to pass through to the OCT assembly. Electrical conduits or wires 122provide electrically couple the ultrasound transducer 120 to a powersource (not shown) and to an ultrasound receiver (not shown).

FIG. 5 illustrates another embodiment of the invention, wherein anultrasound transducer 120 is formed on or as a part of the ferrule 114of the OCT assembly. FIG. 6 provides a perspective view of the ferrule114 with the ultrasound transducer 120 embedded with a wall of theferrule 114. Similar to the embodiment illustrated in FIG. 4, in thisembodiment, conduits or wires 122 provide power to the ultrasoundtransducer 120 and electrically connect the transducer to the ultrasoundreceiver (not shown).

FIG. 7 illustrates another embodiment of the invention, wherein theultrasound transducer 120 is positioned distal to the OCT assembly andis generally forward-looking. In this embodiment, wires 122 extendacross the OCT assembly and connect to the ultrasound transducer 120 toprovide power.

Turning to FIGS. 8 and 9 the optical fiber 106 described above is formedof a core 140 and two layers, a cladding 142 layer and a buffer 144layer, surrounding the core 140. At least two electrical conduits orwires 146 are operably associated with wall surfaces of the buffer layer144, but may, alternatively, be associated with the cladding layer 142or the core 140.

In the preferred embodiment of the present invention, the optical fibercore 140 is formed of glass made from silica. Nonetheless, othermaterials known in the art, such as fluorozirconate, fluoroaluminate,and chalcogenide glasses, which are used for longer-wavelength infraredapplications, are also within the scope of the present invention. Likeother glasses, these glasses have a refractive index of about 1.5.Typically the difference between core and cladding is less than onepercent.

As known in the art, the cladding 142 may be formed of a material has aslightly lower refractive index (faster speed) in order to keep thelight in the core. The cladding 142 and core 140 make up an opticalwaveguide.

The cladding 142 is usually coated with a tough resin buffer 144 layer,which may be further surrounded by a jacket layer (not shown), usuallyplastic. As known in the art, the buffer material surrounding thecladding of a fiber may be a soft plastic material that protects thecore 140 from damage. These layers add strength to the fiber but do notcontribute to its optical wave guide properties. Rigid fiber assembliessometimes put light-absorbing (“dark”) glass between the fibers, toprevent light that leaks out of one fiber from entering another. Thisreduces cross-talk between the fibers, or reduces flare in fiber bundleimaging applications.

FIG. 8 illustrates one embodiment of the optical fiber 106, wherein thewires 122 (shown in FIGS. 4, 5, and 7 to be interwinding) are embeddedor otherwise coupled on top of the buffer 144 layer of the optical fiber106. The wires may be formed of metal films vacuum deposited onto theoptical fiber or otherwise operably associated with the optical fiber.In another embodiment, as illustrated in FIG. 9, the wires 146 areembedded within the buffer 144 layer of the optical fiber 106.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. Therefore, the scope of the invention is notlimited to the specific exemplary embodiment described above. Allchanges or modifications within the meaning and range of equivalents areintended to be embraced herein.

As used in this application, the articles “a” and “an” refer to one ormore than one (i.e., to at least one) of the grammatical objects of thearticle. By way of example, “an element” means one element or more thanone element.

1-17. (canceled)
 18. An imaging catheter, comprising: an elongateassembly configured to be positioned within a blood vessel, the elongateassembly comprising: a sheath comprising a lumen; and a driveshaftpositioned within the lumen and configured to rotate relative to thesheath; an optical coherence tomography (OCT) assembly coupled to adistal portion of the driveshaft and comprising a surface, wherein theOCT assembly is configured to transmit optical energy in a directionrelative to the surface; and an intravascular ultrasound (IVUS)transducer positioned on the surface of the OCT assembly and configuredto transmit acoustic energy in the direction relative to the surface ofthe OCT assembly such that the OCT assembly and the IVUS transducer areconfigured to scan a same or overlapping area of the blood vessel duringeach segment of a rotation of the driveshaft.
 19. The imaging catheterof claim 18, wherein the OCT assembly comprises a housing, and whereinthe surface forms part of the housing.
 20. The imaging catheter of claim19, wherein the housing comprises an at least partially curved shape,and wherein the surface forms part of the at least partially curvedshape.
 21. The imaging catheter of claim 18, wherein the OCT assemblyand the IVUS transducer are configured to scan the same or overlappingarea of the blood vessel through a wall of the sheath.
 22. The imagingcatheter of claim 18, wherein the driveshaft extends a length of theelongate assembly from a proximal portion of the elongate assembly to adistal portion of the elongate assembly.
 23. The imaging catheter ofclaim 22, further comprising at least one optical fiber coupled to theOCT assembly and at least one conductor coupled to the IVUS transducer,wherein the at least one optical fiber and the at least one conductorextend the length of the elongate assembly.
 24. The imaging catheter ofclaim 23, further comprising: at least one stationary optical fiberpositioned proximal to the at least one optical fiber; and a rotaryoptical fiber connector configured to couple the at least one opticalfiber to the at least one stationary optical fiber such that opticalsignals are transmitted through the at least one optical fiber to the atleast one stationary optical fiber while the at least one optical fiberis rotating.
 25. The imaging catheter of claim 18, further including aguidewire lumen at a distal portion of the sheath.
 26. The imagingcatheter of claim 25, wherein the guidewire lumen includes a firstopening at a distal end of the sheath, and a second opening extendingthrough a wall of the sheath.
 27. The imaging catheter of claim 18,wherein the OCT assembly includes a housing and an imaging portextending through a wall of the housing, and wherein the OCT assembly isconfigured to transmit the optical energy through the imaging port inthe direction.
 28. The imaging catheter of claim 18, wherein the OCTassembly comprises a GRIN lens assembly.
 29. An intraluminal imagingsystem, comprising: the imaging catheter of claim 18; and a displayoperably coupled to the IVUS transducer and the OCT assembly, whereinthe display is configured to concurrently display signals received fromeach of the IVUS transducer and the OCT assembly in registration witheach other.